The present invention relates to a data structure for image transmission, an image coding method, an image decoding method, an image coding apparatus, an image decoding apparatus, a data storage medium which contains a program for implementing an image decoding process, and a data storage medium which contains a coded image signal.
More particularly, the invention relates to a data structure for image transmission that makes coded image signals decodable by decoding processes corresponding to a single coding method, which coded image signals have different data structures obtained by coding digital image signals corresponding to different schemes. Further, the invention relates to an image coding method and an image coding apparatus for generating a coded image signal having the above-described data structure for image transmission, and an image decoding method and an image decoding apparatus for decoding a coded image signal having the data structure for image transmission.
Furthermore, the invention relates to a data storage medium containing a program for implementing the decoding process according to the above-described image decoding method, and a data storage medium containing a coded image signal having the above-described data structure for image transmission.
In order to store or transmit digital image information with high efficiency, it is necessary to compressively code the digital image information. As a typical method for compressive coding of digital image information, there is DCT (Discrete Cosine Transformation) represented by JPEG (Joint Photographic Experts Group) and MPEG (Moving Picture Experts Group). Besides, there are waveform coding methods such as sub-band coding, wavelet coding, and fractal coding.
Further, in order to eliminate redundant image information between display images, such as adjacent frames, inter-frame prediction using motion compensation is carried out. That is, a pixel value of a pixel in the present frame is expressed using a difference between this pixel value and a pixel value of a pixel in the previous frame, and this difference signal is subjected to waveform coding.
To be specific, an arithmetic encoder 10a as shown in FIG. 22(a) is employed for coding a binary image signal S2 which represents a display image of binary information and is obtained from a scanner of a facsimile machine or the like. For decoding a coded binary signal E2, an arithmetic decoder 10b is employed as shown in FIG. 22(b). The arithmetic encoder 10a encodes the binary image signal S2 by an arithmetic coding process which is used when transmitting a facsimile signal, such as MMR (Modified Modified Reed) or JBIG (Joint Bi-level Image Coding Experts Group), thereby generates a coded binary signal E2. The arithmetic decoding apparatus 10b decodes the coded binary signal E2 by an arithmetic decoding process corresponding to the arithmetic coding process, thereby regenerates a decoded binary signal D2.
As shown in FIG. 22(c), a coded binary signal 600a (E2) corresponding to one display image includes a synchronous signal 601 at the beginning, a header 603 that follows signal 601, and shape data 604 that follows the header 603.
Further, an image coding apparatus 20 shown in FIG. 23(a) is employed for coding a digital image signal St treated in MPEG2, and an image decoding apparatus 25 shown in FIG. 23(b) is employed for decoding a coded image signal Et. The digital image signal St treated in MPEG2 is a rectangle image signal which includes a luminance signal and a color difference signal for color display (gradation display), and information showing the horizontal and vertical size of an image on one display image (one frame). The image coding apparatus 20 comprises an information source encoder 20a which subjects the digital image signal (rectangle image signal) St to information source coding, and a variable-length encoder 20b which subjects the output from the encoder 20a to variable-length coding to generate a coded image signal (coded pixel value signal) Et. The image decoding apparatus 25 comprises a variable-length decoder 25b which subjects the coded image signal Et to variable-length decoding, and an information source decoder 25a which subjects the output from the decoder 25b to information source decoding to generate a decoded image signal (decoded pixel value signal) Dt.
The information source encoder 20a comprises a DCT processor 21 which subjects each of plural blocks, into which a display image (one frame) is divided, to DCT (Discrete Cosine Transform), and a quantizer 22 which quantizes the output from the DCT processor 21. The information source decoder 25a comprises an inverse quantizer 26 which inversely quantizes the output from the variable-length decoder 25b, and an IDCT processor 27 which subjects the output from the decoder 25b to inverse DCT. As shown in FIG. 23(c), a coded image signal 700a (Et) corresponding to one display image includes a 32-bit synchronous signal 701 at the beginning, a header 703 that follows signal 701, and coded pixel value bit streams (coded texture bit streams) 71C1, 71C2, 71C3, . . . corresponding to blocks C1, C2, C3, . . . , into which the display image is divided, respectively. The coded texture bit streams 71C1, 71C2, and 71C3 include 5-bit quantization scales 704, 707, and 710, variable-length texture motion vectors (MV) 705, 708, and 711, and variable-length texture DCT coefficients 706, 709, and 712, respectively.
In recent years, a method for compressively coding and transmitting an image signal in the basis of individual object has been put to practical use. More specifically, an image, corresponding to one display image and composed of plural objects, is subjected to compressive coding and transmission in an object-wise manner, thereby increases the data compression ratio and enables decoding/reproducing of the objects separately. In this method, on the reproduction end, coded image signals corresponding to the respective objects are decoded and reproduced, and the reproduced image signals are synthesized to display an image corresponding to one display image. This object-by-object coding enables the user to freely combine images of objects to be displayed, whereby editing of a moving picture is facilitated. Furthermore, in this method, it is possible to display a moving picture without reproducing images of relatively unimportant objects, according to the congestion of the transmission line, the performance of reproduction apparatus, and the preference of the viewer. In other words, scalability in object units, i.e., to change the contraction scale of image display for each object, is realized.
In the object-by-object compressive coding of an image signal, since the respective objects have different shapes, an image signal of an arbitrary shape image (hereinafter, referred to as an arbitrary shape image signal) is subjected to compressive coding. The arbitrary shape image signal includes a texture signal (pixel value signal) for color display of an object (gradation display) and comprising a luminance signal and a color difference signal, and a shape signal representing the shape of an image. The shape signal indicates whether each pixel as a component of a display region is located outside the object or inside the object, and it is expressed by binary digit.
Further, there is a case where the arbitrary shape image signal includes transparency information representing the transparency of an object when the object is placed as a foreground image on a background image, in addition to the texture signal and the shape signal. The transparency information is usually expressed by a multivalued transparent signal of at least three bits. A combination of the binary shape signal (binary transparency signal) and the multivalued transparency signal is called a transparency signal. The multivalued transparency signal in the transparency signal is treated identically to a texture signal in the following coding process.
When an arbitrary shape image signal including both of a texture signal and a binary shape signal is coded, initially, the shape signal is coded and, thereafter, the texture signal is coded. In MPEG4, coding, transmission, and decoding of such an arbitrary shape image signal are being standardized, and FIG. 24(a) is a block diagram showing an image coding apparatus which performs a coding process currently being standardized as MPEG4.
In FIG. 24(a), reference numeral 200a designates an image coding apparatus which extracts an arbitrary shape image signal Sp corresponding to each of plural objects constituting a display image, according to a video signal Sv output from a camera or an image recording/reproduction apparatus (VTR), and encodes the arbitrary shape image signal.
The image coding apparatus 200a includes a chromakey processor 201 which subjects the video signal Sv to a chromakey process as follows. Initially, the chromakey processor 201 separates an arbitrary shape image signal corresponding to each object from a background image signal to a shape signal Spk representing the shape of the object as binary information and a texture signal (pixel value signal) Spt for color display of the object and comprising a luminance signal and a color difference signal. Then, the chromakey processor 201 outputs the signals Spk and Spt for each of plural blocks into which a display region corresponding to each object on the display image is divided. When outputting the signals Spk and Spt, the chromakey processor 201 outputs a switch timing signal Ts representing the timing of switching between the shape signal Spk and the texture signal Spt. Further, the image coding apparatus 200a includes an arithmetic encoder 120a which codes the shape signal Spk, block by block, by arithmetic coding (refer to JBIG); an information source encoder 130a which performs DCT and quantization of the texture signal Spt block by block; and a variable-length encoder 139 which performs variable-length coding of the output from the information source encoder 130a. 
Further, the image coding apparatus 200a includes a switch 202 which connects the output from the chromakey processor 201 with one of the input of the arithmetic encoder 120a and the input of the information source encoder 130a, in response to a switch timing signal Ts; and a multiplexer 150 which multiplexes a coded shape bit stream Epk output from the arithmetic encoder 120a and a coded texture bit stream Ept output from the variable-length encoder 139 together with other necessary signals. As shown in FIG. 24(c), a coded arbitrary shape signal Ep (500a), in which coded shape bit streams (Epk) 51A1, 51A2, and 51A3, coded texture bit streams (Ept) 52A1, 52A2, and 52A3, and other necessary signals are arranged in prescribed order, is output from the multiplexer 150.
The above-described arithmetic coding process is adopted in a method of transmitting a facsimile signal, such as MMR or JBIG, and the above-described DCT process is adopted in the MPEG standard. As shown in FIG. 24(c), the coded data of each of blocks A1, A2 and A3 is composed of the coded shape bit stream Epk and the coded texture bit stream Ept.
In the coding apparatus 200a so constructed, the video signal Sv is processed by the chromakey processor 201, and an arbitrary shape image signal Sp corresponding to each object is output from the chromakey processor 201. The shape signal Spk included in the arbitrary shape image signal Sp is input to the arithmetic encoder 120a by the switch 202 controlled by the switch timing signal Ts, coded by the encoder 120a, and output as a coded shape bit stream Epk toward the multiplexer 150. On the other hand, the texture signal Spt included in the arbitrary shape image signal Sp is input to the information source encoder 130a by the switch 202 controlled by the switch timing signal Ts, subjected to DCT and quantization in the encoder 130a, and output as a coded texture bit stream Ept toward the multiplexer 150. The coding of the shape signal Spk and the coding of the texture signal Spt are carried out block by block.
In the multiplexer 150, the coded shape bit stream Epk, the coded texture bit stream Ept, and other required signals are arranged in prescribed order, and these streams and signals are output from the multiplexer 150 as a coded arbitrary shape signal Ep.
The image decoding apparatus 200b shown in FIG. 24(b) is used for decoding of the arbitrary shape signal Ep which has been coded by the image coding apparatus 200a. 
The image decoding apparatus 200b comprises a data analyzer 160 which analyzes the coded arbitrary shape signal Ep and outputs a control signal SWb; an arithmetic decoder 170a which subjects the coded shape bit stream Epk included in the coded arbitrary shape signal Ep to block-by-block arithmetic decoding, and generates an end timing signal Te when arithmetic decoding of one block has ended; an information source decoder 180a which subjects the coded texture bit stream Ept included in the coded arbitrary shape signal Ep to information source decoding, i.e., inverse DCT and inverse quantization; a switch 101b which supplies the coded arbitrary shape signal Ep output from the data analyzer 160 to either the arithmetic decoder 170a or the information source decoder 180a, in response to the control signal SWb and the end timing signal Te; and a synthesizer 190 which synthesizes outputs Dpk and Dpt from the decoders 170a and 180a and outputs the synthesized signal as a decoded arbitrary shape signal Dp.
In the image decoding apparatus 200b so constructed, receiving the coded arbitrary shape signal Ep, the data analyzer 160 analyzes information included in this signal, and outputs the control signal SWb toward the switch 101b when it detects the last bit of the texture bit stream Ept. In response to the control signal SWb, the switch 101b supplies the output from the data analyzer 160 to the arithmetic decoder 170a. The arithmetic decoder 170a decodes the coded shape bit stream Epk, and outputs the end timing signal Te when decoding of the coded shape bit stream Epk corresponding to each block has ended. When the end timing signal Te is input to the data analyzer 160, the data analyzer 160 outputs the control signal SWb to the switch 101b, and the switch 101b connects the output of the data analyzer 160 to the information source decoder 180a. The information source decoder 180a decodes one block of the coded texture signal Ept included in the coded arbitrary shape signal Ep. The synthesizer 190 synthesizes the output from the arithmetic decoder 170a and the output from the information source decoder 180a, and outputs the decoded arbitrary shape signal Dp as a reproduced signal. When the above-mentioned decoding process has been completed for the coded arbitrary shape signal Ep corresponding to one object to generate the decoded arbitrary shape signal Dp corresponding to the object, image display of the object is possible.
Although no description is given of processing of an arbitrary shape image signal including a multivalued transparency signal (arbitrary shape image signal with transparency information) with respect to FIGS. 24(a)-24(c), the multivalued transparency signal is processed in the same manner as the texture signal (pixel value signal) if the arbitrary shape image signal includes a multivalued transparency signal.
As described above, in the conventional method of coding an image signal, the arithmetic coding method employed in JBIG or the like is used for coding of a binary image signal, i.e., a binary shape signal, while the information source coding method employed in MPEG2 or the like is used for coding of a digital image signal for color display of an image, i.e., a texture signal. Further, the coding method of MPEG4, i.e., combination of arithmetic coding and information source coding is used for coding of an image signal including a binary shape signal and a texture signal.
It is a matter of course that, when decoding coded signals obtained by different coding methods, different decoding methods corresponding to the respective coding methods should be employed. In other words, since different coding methods are used for coding different kinds of image signals in the conventional coding process, different data analysis methods should be employed in the decoding process of the coded signals.
Although an image decoding apparatus based on MPEG4 is able to decode any of coded signals of a binary image signal (JBIG), a digital image signal (MPEG2), and an arbitrary shape image signal (MPEG4), this apparatus has the following drawbacks.
In a coded arbitrary shape signal obtained by block-by-block coding of an arbitrary shape image signal, coded shape bit streams corresponding to the respective blocks and coded texture bit streams corresponding to the respective blocks are alternatingly arranged. On the other hand, in a coded binary signal obtained by block-by-block coding of a binary image signal, coded shape bit streams corresponding to the respective blocks are successively arranged. Therefore, in the data analysis method (data analyzer) according to MPEG4, the above-described control signal SWb cannot be generated by analysis of the coded binary image signal containing no coded texture bit stream, as such the coded shape bit streams of the respective blocks in the coded binary signal cannot be successively output toward the arithmetic decoder 170a. To be specific, in the image decoding apparatus 200b, when processing of a coded shape bit stream corresponding to some block has ended, the end timing signal Te is output from the arithmetic decoder 170a toward the switch 101b, whereby the switch 101b supplies the bit stream from the data analyzer 160 to the information source decoder 180a. However, since no coded texture bit stream is included in the coded binary signal, the data analyzer 160 cannot generate the control signal SWb for controlling the switch 101b so that the bit stream is input to the arithmetic decoder 170a, and a coded shape bit stream corresponding to the next block is input to the information source decoder 180a. 
Hence, to support coding of the binary image signal, a dummy texture bit stream corresponding to the block is added using the conventional method after the coded shape bit stream of each block, thereby making the data structure of the coded binary signal apparently identical to the data structure of the coded arbitrary shape signal. In this case, the coded binary signal can be analyzed by the data analysis method based on MPEG4 and decoded by the image decoding process based on MPEG4.
However, since the coded dummy texture bit stream is added to the coded shape bit stream when the coded binary image signal is output, the bit number is wasted in the coding process, resulting in a reduction in the coding efficiency.
In the decoding process based on MPEG4, a coded image signal (coded pixel value signal), which is obtained by coding a digital image signal (rectangle image signal) corresponding to MPEG2 and comprising only a texture signal, is decodable as well as a coded arbitrary shape signal obtained by coding an arbitrary shape image signal. The reason is as follows. In a coded image signal including coded texture bit streams, since starting point and end point of the coded texture bit stream corresponding to each block is detectable, the switch 101b can be controlled by the control signal SWb so that the coded texture bit stream is always input to the information source decoder 180b. 
Further, in the decoding process corresponding to the coding process based on MPEG4, if the processing is overloaded, when decoding a coded arbitrary shape signal obtained by coding an arbitrary shape image signal, both of the coded shape bit stream and the coded texture bit stream corresponding to each block cannot be decoded within a display time that is set in advance, as such the motion of image on the display lacks of smoothness or stops.
An object of the present invention is to provide a data structure for image transmission, an image decoding method, and an image decoding apparatus, which enable decoding of coded image signals having different data structures obtained by coding digital image signals corresponding to different schemes or the like, by decoding processes corresponding to a single coding method, for example, those capable of decoding both of a binary image signal and an arbitrary shape image signal, without increasing the bit number during the coding process.
Another object of the present invention is to provide a data storage medium containing a program for implementing the decoding processes according to the above-described image decoding method, and a data storage medium containing a coded image signal having the above-mentioned data structure for image transmission.
Still another object of the present invention is to provide an image coding method and an image coding apparatus, which can create a coded image signal having a data structure for image transmission, which data structure enables decoding of coded image signals having different data structures obtained by coding digital image signals corresponding to different schemes or the like by decoding processes corresponding to a single coding method, for example, decoding of a binary image signal and an arbitrary shape image signal without increasing the bit number during the coding process.
Yet another object of the present invention is to provide an image decoding apparatus which can reproduce a coded image signal by decoding while maintaining a smooth motion of image on a display screen even when the load of an arithmetic processor performing the decoding is large.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a first aspect of the present invention, there is provided a data structure for transmitting a coded image signal obtained by coding a digital image signal, including:
at least coded shape bit streams between the following two kinds of bit streams: coded shape bit streams obtained by coding a shape signal which represents a display image of binary information or the shape in binary format of each object as one of the components of a display image; and coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the object; and
an image identifier for deciding whether the coded image signal includes, as the coded bit streams, both of the coded shape bit streams and the coded pixel value bit streams, or only the coded shape bit streams;
wherein the image identifier and the coded bit streams are arranged so that the image identifier is followed by the coded bit streams.
Therefore, by referring to the image identifier, a coded signal including no coded pixel value bit streams can be analyzed using a data analysis method for a coded signal including coded pixel value bit streams.
According to a second aspect of the present invention, in the above-described data structure for image transmission, the image identifier comprises a 2-bit code. Therefore, it is possible to realize decoding processes for four kinds of coded image signals including a coded binary signal and a coded arbitrary shape signal, corresponding to a single coding method.
According to a third aspect of the present invention, there is provided an image coding method receiving a digital image signal, and subjecting the digital image signal to a coding process according to the data structure of the digital image signal, wherein:
it is decided whether the digital image signal is a binary image signal including, as data for display, only a shape signal representing a display image of binary information, or an arbitrary shape image signal including, as data for display, both of a shape signal representing the shape of each object as one of the components of a display image and a pixel value signal representing the gradation of the object;
for the binary image signal, the shape signal is subjected to a first coding process and, in the coding process, an image identifier having a first value is generated, thereby creating a coded binary signal including the image identifier;
for the arbitrary shape image signal, the shape signal is subjected to the first coding process while the pixel value signal is subjected to a second coding process employing a coding method different from that of the first coding process and, in the coding process, an image identifier having a second value is generated, thereby creating a coded arbitrary shape signal including the image identifier; and
in response to the input digital image signal, one of the coded binary signal and the coded arbitrary shape signal is output.
Therefore, even though image signals having different data structures are coded by different coding methods, these coded image signals can be decoded in decoding processes corresponding to a single coding method. In addition, the bit number hardly increases during the coding process.
According to a fourth aspect of the present invention, in the above-described image coding method, the image identifier comprises a 2-bit code. Therefore, coding processes for four kinds of image signals including a binary image signal and an arbitrary shape image signal are carried out so that coded signals corresponding to these image signals can be identified at the decoding end.
According to a fifth aspect of the present invention, there is provided an image coding apparatus receiving a digital image signal, and subjecting the digital image signal to a coding process according to the data structure of the digital image signal, comprising:
signal identification means for receiving the digital image signal, and deciding whether the digital image signal is a binary image signal including, as data for display, only a shape signal showing a display image of binary information, or an arbitrary shape image signal including, as data for display, both of a shape signal showing the shape of each object as one of the components of a display image and a pixel value signal representing the gradation of the object, and outputting an identifier signal according the result of the decision;
signal extraction means for extracting the shape signal from the binary image signal, and the shape signal and the pixel value signal from the arbitrary shape image signal;
first coding means for coding the shape signals by a first coding process to generate coded shape bit streams;
second coding means for coding the pixel value signal by a second coding process employing a coding method different from that of the first coding process, thereby generating coded pixel value bit streams;
signal supply means for selecting, according to the identifier signal, one of first and second operations, where the first operation is to supply the shape signal of the binary image signal to the first coding means and the second operation is to supply the shape signal of the arbitrary shape image signal to the first coding means while supplying the pixel value signal of the arbitrary shape image signal to the second coding means; and
multiplexing means for multiplexing the identifier signal from the signal identification means, the coded shape bit streams output from the first coding means, and the coded pixel value bit streams output from the second coding means;
wherein a coded binary signal including the identifier signal and the coded shape bit streams is output when the binary image signal is input as the digital image signal, and a coded arbitrary shape signal including the identifier signal, the coded shape bit streams, and the coded pixel value bit streams is output when the arbitrary shape image signal is input as the digital image signal.
Therefore, even though image signals having different data structures are coded by different coding methods, these coded signals can be decoded in decoding processes corresponding to a single coding method. In addition, the bit number hardly increases during the coding process.
According to a sixth aspect of the present invention, there is provided an image decoding method receiving, as a coded signal obtained by coding a digital image signal, a coded image signal having an image identifier according to the data structure of the digital image signal, and subjecting the coded image signal to a decoding process according to the data structure, wherein:
the coded image signal is analyzed with reference to the image identifier to decide whether the coded image signal is a coded arbitrary shape signal including, as data for display, both of coded shape bit streams obtained by coding a shape signal which represents the shape of each object as one of the components of a display image and coded pixel value bit streams obtained by coding of a pixel value signal representing the gradation of the object, or a coded binary signal including, as data for display, only coded shape bit streams obtained by coding a shape signal representing a display image of binary information;
when the input coded image signal is the coded arbitrary shape signal, decoding of the coded shape bit streams thereof by a first decoding method, and decoding of the coded pixel value bit streams thereof by a second decoding method, are carried out according to the arrangement of these bit streams; and
when the input coded image signal is the coded binary signal, only decoding of the coded shape bit streams thereof by the first coding method is carried out.
Therefore, even though image signals having different data structures are coded by different coding methods, these coded image signals can be decoded in decoding processes corresponding to a single coding method. In addition, the bit number hardly increases during the coding process.
According to a seventh aspect of the present invention, in the above-described image decoding method, the image identifier comprises a 2-bit code. Therefore, it is possible to decode four kinds of coded image signals including a coded binary signal and a coded arbitrary shape signal, in decoding processes corresponding to a single coding method.
According to an eighth aspect of the present invention, there is provided an image decoding apparatus receiving, as a coded signal obtained by coding a digital image signal, a coded image signal having an image identifier according to the data structure of the digital image signal, and subjecting the coded image signal to a decoding process according to the data structure, comprising:
data analysis means for deciding whether the coded image signal is a coded arbitrary shape signal including, as data for display, both of coded shape bit streams obtained by coding a shape signal which represents the shape of each object as one of the components of a display image and coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the object, or a coded binary signal including, as data for display, only coded shape bit streams obtained by coding a shape signal representing a display image of binary information;
first decoding means for decoding the coded shape bit streams by a first decoding process to generate a decoded shape signal;
second decoding means for decoding the coded pixel value bit streams by a second decoding process employing a decoding method different from that of the first decoding process, thereby generating a decoded pixel value signal;
signal switch means for supplying the coded image signal to one of the first and second decoding means, according to a switch control signal;
the data analysis means supplying a first switch control signal to the signal switch means when the coded image signal is the coded binary signal, and supplying a second switch control signal to the signal switch means when the coded image signal is the coded arbitrary shape signal; and
the signal switch means being in the fixed switching state where the coded shape bit streams of the coded binary signal are input to the first decoding means alone when it receives the first switch control signal, and being in the alternate switching state where, according to the arrangement of the coded shape bit streams and the coded pixel value bit streams in the coded arbitrary shape signal, the coded shape bit streams are input to the first decoding means while the coded pixel bit streams are input to the second deciding means, when it receives the second switch control signal.
Therefore, even though image signals having different data structures are coded by different coding methods, these coded image signals can be decoded in decoding processes corresponding to a single coding method. In addition, the bit number hardly increases during the coding process.
According to a ninth aspect of the present invention, the above-described image decoding apparatus further comprises over-load detection means for detecting that the load on the decoding process by one of the first and second decoding means exceeds a threshold value which is set in advance, and outputting an over-load detection signal toward the data analysis means:
wherein, when the over-load detection signal is input to the data analysis means, the data analysis means outputs a third switch control signal toward the signal switch means; and
in response to the third switch control signal, the signal switch means supplies either of the coded shape bit streams and the coded pixel value bit streams in the coded arbitrary shape signal to one of the first and second decoding means.
Therefore, coded image signals having different data structures can be decoded in decoding processes corresponding to a single coding method, and the bit number hardly increases during the coding process. Further, even when a processor for decoding is over-loaded, the coded image signals are reproduced by the decoding processes while maintaining smooth motion of image on the display screen.
According to a tenth aspect of the present invention, the above-described image decoding apparatus further comprises control signal input means for inputting a manual control signal from the outside to the data analysis means:
wherein, when the data analysis means receives the manual control means, it outputs a third switch control signal toward the signal switch means; and
in response to the third switch control signal, the signal switch means supplies the coded shape bit streams of the coded arbitrary shape signal to the first decoding means, and does not supply the coded pixel value bit streams to the second decoding means.
Therefore, coded image signals having different data structures can be decoded in decoding processes corresponding to a single coding method, and the bit number hardly increases during the coding process. Further, when image data stored in a recording medium are retrieved, only decoding of coded shape bit streams is continued until an object image is found, whereby the data retrieval is carried out quickly.
According to an eleventh aspect of the present invention, there is provided a data structure for transmitting a coded image signal obtained by coding a digital image signal, including:
at least one of the following two kinds of coded bit streams: coded shape bit streams obtained by coding a shape signal which represents a display image of binary information or the shape in binary format of each object as one of the components of a display image, and coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the display image or the object; and
an image identifier comprising a multiple-bit code, for deciding whether the coded image signal includes, as the coded bit streams, at least the coded shape bit streams, or only the coded pixel value bit streams;
wherein the image identifier and the coded bit streams are arranged so that the image identifier is followed by the coded bit streams.
Therefore, by referring to the image identifier, at least a coded image signal including coded shape bit streams and a coded image signal including no coded shape bit streams can be identified among various kinds of coded image signals.
According to a twelfth aspect of the present invention, there is provided an image decoding method receiving, as a coded signal obtained by coding a digital image signal, a coded image signal having an image identifier according to the data structure of the digital image signal, and subjecting the coded image signal to a decoding process according to the data structure, wherein:
the coded image signal is analyzed with reference to the image identifier to decide which of the following three coded signals is the coded image signal;
a coded arbitrary shape signal including, as data for display, both of coded shape bit streams obtained by coding a shape signal which represents the shape of each object as one of the components of a display image, and coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the object,
a coded pixel value signal including, as data for display, only coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of a display image, and
a coded binary signal including, as data for display, only coded shape bit streams obtained by coding a shape signal representing a display image of binary information;
when the input coded image signal is the coded pixel value signal, decoding of the coded pixel value bit streams thereof is carried out; and
when the input coded image signal is the coded binary signal or the coded arbitrary shape signal, decoding of the coded bit streams included in these signals is stopped.
Therefore, among a coded binary signal, a coded arbitrary shape signal, and a coded rectangle signal (coded pixel value signal), only the coded rectangle signal can be selected and decoded by a decoding apparatus for decoding only the coded rectangle signal which is obtained by coding a pixel value signal for color display of image.
According to a thirteenth aspect of the present invention, there is provided an image decoding apparatus receiving, as a coded signal obtained by coding a digital image signal, a coded image signal having an image identifier according to the data structure of the digital image signal, and subjecting the coded image signal to a decoding process according to the data structure, comprising:
data analysis means for analyzing the coded image signal according to the image identifier to decide which of the following three coded signals is the coded image signal;
a coded arbitrary shape signal including, as data for display, both of coded shape bit streams obtained by coding a shape signal which represents the shape of each object as one of the components of a display image, and coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the object,
a coded pixel value signal including, as data for display, only coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of a display image, and
a coded binary signal including, as data for display, only coded shape bit streams obtained by coding a shape signal representing a display image of binary information;
decoding means for decoding the coded pixel value bit streams to generate a decoded pixel value signal;
signal discarding means for discarding the coded image signal;
signal switch means for supplying the coded image signal to one of the decoding means and the signal discarding means according to a switch control signal;
the data analysis means supplying a first switch control signal to the signal switch means when the coded image signal is the coded pixel value signal, and supplying a second switch control signal to the signal switch means when the coded image signal is the coded arbitrary shape signal or the coded binary signal; and
the signal switch means supplying the coded pixel value bit streams of the coded pixel value signal to the decoding means when it receives the first switch control signal, and supplying the coded bit streams included in the coded arbitrary shape signal and the coded binary signal to the signal discarding means when it receives the second switch control signal.
Therefore, among a coded binary signal, a coded arbitrary shape signal, and a coded rectangle signal (coded pixel value signal), only the coded rectangle signal can be selected and decoded by a decoding apparatus for decoding only the coded rectangle signal which is obtained by coding a pixel value signal for color display of image.
According to a fourteenth aspect of the present invention, there is provided a data structure for transmitting a coded image signal obtained by coding a digital image signal, including:
at least one of the following three kinds of coded bit streams: coded shape bit streams obtained by coding a shape signal which represents a display image of binary information or the shape in binary format of each object as one of the components of a display image; coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the display image or the object; and coded transparency bit streams obtained by coding a multivalued transparency signal representing the transparency of the object; and
an image identifier comprising a multiple-bit code, for deciding which of the following four coded image signals is the coded image signal;
a coded pixel value signal including, as the coded bit streams, only the coded pixel value bit streams,
a first coded arbitrary shape signal including, as the coded bit streams, the coded shape bit streams and the coded pixel value bit streams,
a coded binary signal including, as the coded bit streams, only the coded shape bit streams, and
a second coded arbitrary shape signal including, as the coded bit streams, the coded shape bit streams, the coded pixel value bit streams, and the coded transparency bit streams;
wherein the image identifier and the coded bit streams are arranged so that the image identifier is followed by the coded bit streams.
Therefore, by referring to the image identifier, among various kinds of coded image signals, a coded image signal including at least one of coded shape bit streams, coded pixel value bit streams, and coded transparency bit streams can be identified.
According to a fifteenth aspect of the present invention, there is provided an image decoding method receiving, as a coded signal obtained by coding a digital image signal, a coded image signal having an image identifier according to the data structure of the digital image signal, and subjecting the coded image signal to a decoding process according to the data structure, wherein:
the coded image signal is analyzed with reference to the image identifier to decide which of the following four coded signals is the coded image signal;
a first coded arbitrary shape signal including, as data for display, coded shape bit streams obtained by coding a shape signal representing the shape of each object as one of the components of a display image, and coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the object,
a second coded arbitrary shape signal including, as data for display, in addition to coded shape bit streams and coded pixel value bit streams, coded transparency bit streams obtained by coding a multivalued transparency signal representing the transparency of the object,
a coded pixel value signal including, as data for display, only coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of a display image, and
a coded binary signal including, as data for display, only coded shape bit streams obtained by coding a shape signal representing a display image of binary information;
when the input coded image signal is the first coded arbitrary shape signal, decoding of the coded shape bit streams thereof by a first decoding method, and decoding of the coded pixel value bit streams thereof by a second decoding method, are carried out according to the arrangement of these bit streams;
when the input coded image signal is the second coded arbitrary shape signal, decoding of the coded shape bit streams thereof by the first decoding method, decoding of the coded pixel value bit streams thereof by the second decoding method, and decoding of the coded transparency bit streams thereof by a third decoding method, are carried out according to the arrangement of these bit streams;
when the input coded image signal is the coded pixel value signal, only decoding of the coded pixel value bit streams thereof by the second decoding method is carried out; and
when the input coded image signal is the coded binary signal, only decoding of the coded shape bit streams thereof by the first decoding method is carried out.
Therefore, for example, the first and second coded arbitrary shape signal, the coded rectangle signal (coded pixel value signal), and the coded binary signal can be decoded by the first to third decoding methods corresponding to three coded bit streams included in the second coded arbitrary shape signal.
According to a sixteenth aspect of the present invention, there is provided a data structure for transmitting a coded image signal obtained by coding a digital image signal, including:
at least one of the following three kinds of coded bit streams: coded shape bit streams obtained by coding a shape signal which represents a display image of binary information or the shape in binary format of each object as one of the components of a display image, coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the display image or the object, and coded transparency bit streams obtained by coding a multivalued transparency signal representing the transparency of the object; and
an image identifier comprising a multiple-bit code, for deciding which of the following five coded image signals is the coded image signal;
a coded pixel value signal including, as the coded bit streams, only the coded pixel value bit streams,
a first coded arbitrary shape signal including, as the coded bit streams, the coded shape bit streams and the coded pixel value bit streams,
a coded binary signal including, as the coded bit streams, only the coded shape bit streams,
a second coded arbitrary shape signal including, as the coded bit streams, the coded shape bit streams, the coded pixel value bit streams, and the coded transparency bit streams, and
a coded transparency signal including, as the coded bit streams, the coded shape bit streams and the coded transparency bit streams;
wherein the image identifier and the coded bit streams are arranged so that the image identifier is followed by the coded bit streams.
Therefore, by referring to the image identifier, among various kinds of coded image signals, a coded image signal including at least one of coded shape bit streams, coded pixel value bit streams, and coded transparency bit streams can be identified.
According to a seventeenth aspect of the present invention, there is provided an image decoding method receiving, as a coded signal obtained by coding a digital image signal, a coded image signal having an image identifier according to the data structure of the digital image signal, and subjecting the coded image signal to a decoding process according to the data structure, wherein:
the coded image signal is analyzed with reference to the image identifier to decide which of the following five coded signals is the coded image signal;
a first coded arbitrary shape signal including, as data for display, coded shape bit streams obtained by coding a shape signal representing the shape of each object as one of the components of a display image, and coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of the object,
a second coded arbitrary shape signal including, as data for display, in addition to coded shape bit streams and coded pixel value bit streams, coded transparency bit streams obtained by coding a multivalued transparency signal representing the transparency of the object,
a coded transparency signal including, as data for display, coded shape bit streams obtained by coding a shape signal representing the shape of the object, and coded transparency bit stream obtained by coding a multivalued signal representing the transparency of the object,
a coded binary signal including, as data for display, only coded shape bit streams obtained by coding a shape signal representing a display image of binary information, and
a coded pixel value signal including, as data for display, only coded pixel value bit streams obtained by coding a pixel value signal representing the gradation of a display image; and
when the input coded image signal is the first coded arbitrary shape signal, decoding of the coded shape bit streams thereof by a first decoding method, and decoding of the coded pixel value bit streams thereof by a second decoding method, are carried out according to the arrangement of these bit streams;
when the input coded image signal is the second coded arbitrary shape signal, decoding of the coded shape bit streams thereof by the first decoding method, decoding of the coded pixel value bit streams thereof by the second decoding method, and decoding of the coded transparency bit streams thereof by a third decoding method, are carried out according to the arrangement of these bit streams;
when the input coded image signal is the coded transparency signal, decoding of the coded shape bit streams thereof by the first decoding method, and decoding of the coded transparency bit streams by the third decoding method, are carried out according to the arrangement of these bit streams;
when the input coded image signal is the coded binary signal, only decoding of the coded shape bit streams thereof by the first decoding method is carried out; and
when the input coded image signal is the coded pixel value signal, only decoding of the coded pixel value bit streams thereof by the second decoding method is carried out.
Therefore, for example, the coded arbitrary shape signal, the coded rectangle signal (coded pixel value signal), the coded binary signal, and the coded transparency signal can be decoded by the first to third decoding methods corresponding to three coded bit streams included in the coded arbitrary shape signal with transparency information.
According to an eighteenth aspect of the present invention, there is provided a data storage medium containing a program for implementing a decoding process of a coded image signal by a computer, the program being constructed so that a decoding process according to any of the above-described image decoding methods is executed by the computer. Therefore, when the program is loaded into the computer, the decoding process according to the above-described decoding method can be implemented by software.
According to a nineteenth aspect of the present invention, there is provided a data storage medium containing a coded image signal obtained by coding a digital image signal, the coded image signal having any of the above-described data structures for image transmission. Therefore, when the stored coded image signals are read from the medium and decoded, these coded image signals, having different data structures, can be identified.